Image signal processing device of image sensor

ABSTRACT

An image-signal processing apparatus ( 1 ) designed to process the signals output from a CCD image sensor ( 10 ) that reads pixel data for one screen, line by line, divides the pixel data into a plurality of channels and outputs the pixel data thus divided. The image-signal processing apparatus ( 1 ) detects and corrects the black level of each pixel data item that the image sensor ( 10 ) has output for one channel. The image-signal processing apparatus ( 1 ) detects and corrects the gain difference between channels, which pertain to the pixel data items output from the image sensor ( 10 ). Hence, the apparatus ( 1 ) can correct the black level of each pixel data item and the gain difference between channels with high accuracy, when used in combination with an image sensor that divides pixel data into a plurality of channels.

TECHNICAL FIELD

[0001] The present invention relates to an image-signal processingapparatus for use in combination with an image sensor that reads pixeldata for one screen, line by line, and divides the pixel data thus read,into a plurality of channels and outputs the pixel data thus divided.

BACKGROUND ART

[0002] CCD image sensors have hitherto been used in video cameras. TheCCD image sensor generates pixel data for one screen, which is acquiredas two-dimensional image data. A vertical register and a horizontalregister read the pixel data, which is converted into one data stream.The data stream is output from one channel. FIG. 1 shows an CCD imagesensor of one-channel output type that transfers data, and also aconventional image-signal processing apparatus of one-channel outputtype, for use in the CCD image sensor.

[0003] As depicted in FIG. 1, the conventional image-signal processingapparatus 101 is designed to process, for example, the image signalsoutput from a CCD image sensor 110. The image sensor comprises avertical register 111 and a horizontal register 112. The verticalregister 111 transfers charges accumulated in an imager in the verticaldirection, in units of lines. The horizontal register 112 transfers thecharges transferred by the vertical register, in the horizontaldirection in units of lines.

[0004] The image-signal processing apparatus 101 comprises an analogfront-end circuit 121, a delay line 122, a Y/C separating circuit 123, aY process circuit 124, and a C process circuit 125. The front-endcircuit 121 receives a signal output from the horizontal register 112 ofthe CCD image sensor 110, performs gain control and A/D conversion onthe signal and outputs a digital image signal. The delay line 122 delaysthe digital pixel data by a predetermined time so that the pixel datamay be subjected to the Y/C separation that will be carried out later.The Y/C separating circuit 123 receives the pixel data input as a RGBsignal or a complementary color signal and separates the pixel data intoa luminance (Y) component and a chroma (C) component. The Y processcircuit 124 effects a prescribed process on the luminance (Y) componentof the pixel data and outputs luminance data. The C process circuit 125carries out a specific process on the chroma (C) component of the pixeldata and outputs chroma data.

[0005] In the image-signal processing apparatus 101 thus configured, theimage signal output in one channel from the CCD image sensor 110 isconverted to a digital signal and the digital signal is separated into aluminance (Y) component and a chroma (C) component. Therefore, theapparatus 101 can output digital image data that consists of thesecomponents. The CCD image sensor 110 may have about 1,000,000 pixels forone screen. In this case, the analog front-end circuit 121 can carry outanalog processes, such as A/D conversion, at an operating frequency ofabout 33 MHz.

[0006] In recent years, CCD image sensors having high resolution of morethan one million pixels for one screen have come into use. If theimage-signal processing apparatus 101 designed to read an one-channeloutput is to read an image signal from a CCD image sensor of such a highresolution exceeding one million pixels, the process of the analogsignal, such as A/D conversion, must be performed at an operatingfrequency exceeding 40 MHz. At such a high frequency, the analog-signalprocess such as A/D conversion is inevitably unstable. To make theprocess stable, it is necessary to use very expensive components such asan IC.

[0007] In order to solve this problem, CCD image sensors with aplurality of output channels have been proposed in recent years. Sinceimage signals are supplied from many output channels, these analogsignals can be processed (or converted to digital signals) at anoperating frequency lower than is required when the CCD image sensor hasonly one channel. The analog process is performed on the signals of allchannels, converting them to digital signals, and the digital signalsare combined into one signal for one channel. Thus, the analog processis stable as is desired.

[0008]FIG. 2 illustrates a conventional image-signal processingapparatus 201 configured to process image signals output from twochannels.

[0009] This image-signal processing apparatus 201 processes imagesignals output from a CCD image sensor 210. The CCD image sensor 210comprises a vertical register 211 and two horizontal register 212 and213. The vertical register 211 transfers charges, generated from lightand accumulated in an imager in the vertical direction, in units oflines. The horizontal registers 212 and 213 transfer the chargestransferred by the vertical register, in the horizontal direction inunits of lines. In the CCD image sensor 210, the charges are transferredfrom the vertical register 211 to the first horizontal register 212 andthe charges are transferred from the first horizontal register 212 tothe second horizontal register 213. Hence, the sensor 210 outputs imagedata items for two lines, respectively, at the same time. For example,the first horizontal register 212 outputs the pixels forming anodd-numbered line, while the second horizontal register 213 outputs thepixels forming an even-numbered line.

[0010] The image-signal processing apparatus 201 comprises a firstanalog front-end circuit 221, a second analog front-end circuit 222, adelay line 223, a Y/C separating circuit 224, a Y process circuit 225,and a C process circuit 226. The first front-end circuit 221 receives asignal output from the first horizontal register 212, performs gaincontrol and A/D conversion on the signal and outputs a digital imagesignal of the first channel. The second front-end circuit 222 receives asignal output from the second horizontal register 213, performs gaincontrol and A/D conversion on the signal and outputs a digital imagesignal of the second channel. The delay line 223 combines the digitalimage signals of the first and second channels, into a one-channel imagesignal. The delay line 223 then delays the one-channel image signal by apredetermined time so that the image signal may be subjected to the Y/Cseparation to be performed later. The Y/C separating circuit 224receives the image signal input as a RGB signal or a complementary colorsignal and separates the image signal into a luminance (Y) component anda chroma (C) component. The Y process circuit 225 carries out aprescribed process on the luminance (Y) component of the image signaland outputs luminance data. The C process circuit 226 effects a specificprocess on the chroma (C) component of the image signal and outputschroma data.

[0011] In the image-signal processing apparatus 201 thus configured, theimage signals output in two channels from the CCD image sensor 210 areconverted to a digital signal. The digital signal is separated into aluminance (Y) component and a chroma (C) component. Thus, the apparatus201 can output a digital image signal that contains a luminance (Y)component and a chroma (C) component. Since the CCD image sensor 210outputs image signals in two channels, the analog front-end circuits 221and 222 only need to have a low operating frequency. This renders theanalog-signal process stable.

[0012] Here arises a problem in manufacturing the CCD images sensor thatoutputs image signals in two channels. It is very difficult to providetwo horizontal registers that are identical in characteristics.Consequently, the signals output in two channels may differ in terms ofgain. Further, they may differ in terms of the black-level offset. Toadjust the gain difference and the black-level offset difference betweenchannels, the horizontal registers hold a pilot signal each, and thepilot signal corrects the gain and black level of each channel. Thepilot signals may have an error, however. Inevitably, it is difficult toadjust the gain difference or the black-level offset difference as isdesired.

DISCLOSURE OF THE INVENTION

[0013] An object of the present invention is to provide an image-signalprocessing apparatus that can correct, with high accuracy, the blacklevel output from an image sensor which outputs image data for onescreen, in a plurality of channels, and which adjusts the gaindifference between channels.

[0014] An image-signal processing apparatus according to this inventionis designed to process an signal output from an image sensor which readspixel data for one screen in units of lines and divides the pixel datareread in units of lines, into a plurality of channels, and outputs thepixel data thus divided. The apparatus comprises: black-level correctingmeans for detecting the black level of the pixel data item for eachchannel, read from the image sensor, and for correcting the black levelof the pixel data item for each channel; and gain correcting means fordetecting and correcting the gain difference between the pixel dataitems for different channels, read by the image sensor.

[0015] In the image-signal processing apparatus, the black levels of thepixel data items that the image sensor has output for the respectivechannels are detected and corrected independently, and the gaindifference between channels is detected and corrected.

[0016] The image-signal processing apparatus according to the inventionis characterized in that the gain correcting means finds an average ofthe pixel data items for a plurality of lines, detects the gaindifference between channels and corrects the gain difference betweenchannels.

[0017] The image-signal processing apparatus of the invention ischaracterized in that the gain correcting means detects the gaindifference for each line in the case where the image sensor outputspixel data items in a plurality of channels for each line. The gaincorrecting means then corrects the gain difference between channels inaccordance with the gain difference thus detected for each line.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a block diagram of a conventional image-signalprocessing apparatus of one-channel output type, for use in combinationwith a CCD image sensor that performs two-channel data transfer;

[0019]FIG. 2 is a block diagram of a conventional image-signalprocessing apparatus of one-channel output type, for use in combinationwith a CCD image sensor that effects two-channel data transfer;

[0020]FIG. 3 is a block diagram of an image-signal processing apparatusaccording to the present invention;

[0021]FIG. 4 is a block diagram the plural-line gain detecting circuitincorporated in the image-signal processing apparatus;

[0022]FIG. 5 is a diagram explaining the operation of the border pixelextracting section provided in the plural-line gain detecting circuit;

[0023]FIG. 6 is a circuit diagram showing the border-pixel integratingsection provided in the plural-line gain detecting circuit;

[0024]FIG. 7 is a diagram for explaining the speed with which theintegrated value converges when the time constant n is changed in theborder-pixel integrating section;

[0025]FIG. 8 is a diagram illustrating the circuit configuration of thegain detecting section incorporated in the plural-line gain detectingcircuit;

[0026]FIG. 9 is a diagram for explaining the process performed by thepixel-rearranging circuit provided in the image-signal processingapparatus; and

[0027]FIG. 10 is a diagram for explaining the process carried out by theone-line gain detecting/correcting circuit provided in the image-signalprocessing apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

[0028] An image-signal processing apparatus that processes an outputsignal of a CCD image sensor of two-channel output type will bedescribed as an embodiment of the invention, with reference to theaccompanying drawings.

[0029]FIG. 3 is a block diagram of an image-signal processing apparatusaccording to the invention.

[0030] The CCD image sensor 10 used in combination with the presentembodiment is an image sensor that divides a one-screen image regionalong a horizontal line, into two parts, and outputs two pixel dataitems from two channels different from each other. More specifically,the CCD image sensor 10 comprises a vertical register 11 and a one-linehorizontal register 12. The vertical register 11 is a register thattransfers the charges accumulated in an imager, in units of lines in thevertical direction. The horizontal register 12 receives the one-linecharge from the vertical register 11 and transfers this charge in unitsof pixels in the horizontal direction, thereby to output the pixel datafrom two channels. The horizontal register 12 divides each line at themidpoint thereof, into two equal parts, and outputs one part from thefirst channel, and the other part from the second channel. The first andsecond channels of he horizontal register 12 shall be referred to as“right channel” and “left channel,” respectively.

[0031] The image-signal processing apparatus 1 comprises a right-channelanalog front-end circuit 21, a left-channel analog front-end circuit 22,a plural-line gain detecting circuit 23, a right-channel black-leveldetecting circuit 24, a left-channel black-level detecting circuit 25, apixel-rearranging circuit 26, a black-level correcting circuit 27, aplural-line gain correcting circuit 28, a one-line gaindetecting/correcting circuit 29, a delay line 30, a Y/C separatingcircuit 31, a Y process circuit 32, and a C process circuit 33.

[0032] The right-channel analog front-end circuit 21 receives an outputsignal from the right channel of the CCD image sensor 10, performs gaincontrol and A/D conversion on the signal and outputs right-channel pixeldata. The right-channel pixel data is supplied from the right-channelanalog front-end circuit 21 to the plural-line gain detecting circuit23, right-channel black-level detecting circuit 24 and pixel-rearrangingcircuit 26.

[0033] The left-channel analog front-end circuit 22 receives an outputsignal from the left channel of the CCD image sensor 10, performs gaincontrol and A/D conversion on this signal and outputs left-channel pixeldata. The left-channel pixel data is supplied from the left-channelanalog front-end circuit 22 to the plural-line gain detecting circuit23, left-channel black-level detecting circuit 25 and pixel-rearrangingcircuit 26.

[0034] The plural-line gain detecting circuit 23 finds the average ofthe right-channel pixel data for a plurality of lines and the average ofthe left-channel pixel data for a plurality of lines. The circuit 23then finds the difference between these averages, thereby obtaining thegain difference between the right and left channels. The gain differencethus obtained is supplied, as a gain-correcting value, to theplural-line gain correcting circuit 28. An example of an operation thatthe plural-line gain detecting circuit 23 performs will be explainedlater.

[0035] The right-channel black-level detecting circuit 24 detects theblack level of the right-channel pixel data. To detect the black level,the difference between any corrected black level and the immediatelyfollowing black level detected, and the average of such differencesaccumulated thus far is calculated. The average thus calculated isoutput as a right-channel black-level correcting value. In other words,a black-level correcting value is obtained by the conversion of dataaccomplished by, for example, an IIR filter. The left-channelblack-level detecting circuit 25 finds a left-channel black-levelcorrecting value in the same way as the right-channel black-leveldetecting circuit 24 finds the right-channel black-level correctingvalue. Therefore, the black levels of the right and left channels wouldnot mix. They can be detected with high precision. The black-levelcorrecting values, thus obtained, are supplied to the black-levelcorrecting circuit 27 and the plural-line gain detecting circuit 23.

[0036] The pixel-rearranging circuit 26 synthesizes the right-channelpixel data and the left-channel pixel data, converting them toone-channel pixel data. The pixel data output from the pixel-rearrangingcircuit 26 represents pixels arranged in the same scanning order as thepixels forming a one-screen image data generated by a CCD image sensorof one-channel output type. Thus rearranged, the pixel data items can beprocessed in the same method as the image-signal processing circuit thatis used in the conventional CCD image sensor of one-channel output type.The one-channel pixel data, thus generated, is supplied to theblack-level correcting circuit 27. An example of an operation that thepixel-rearranging circuit 26 performs will be described later.

[0037] The black-level correcting circuit 27 effects offset addition,adding the black-level correcting values to the one-channel pixel data,thus correcting the black level. Note that the correcting values havebeen obtained by the black-level detecting circuit 24, independently ofeach other for the right channel and the left channel, respectively.Hence, the black levels to be added to each pixel of the one-channelpixel data are switched in accordance with the scanning order (forexample, every other half line). The image data whose black level isthus corrected is supplied to the plural-line gain correcting circuit28.

[0038] The plural-line gain correcting circuit 28 multiplies aone-channel component (e.g., right-channel component) of the one-channelpixel data by the gain-correcting value the plural-line gain detectingcircuit 23 has found. The plural-line gain correcting circuit 28 thuscorrects the gain difference between channels. The gain differencebetween the channel can be corrected if the gain for one channel isvaried on the basis of the gain for the other channel. This is why theplural-line gain correcting circuit 28 multiplies only the component ofone channel component (e.g., right channel) by the gain-correctingvalue. In order to multiply each pixel of only one channel by thegain-correcting value, it suffices to switching the data component ofone channel to the data component of the other channel, and vice versa,in accordance with the scanning order (for example, every other halfline). The pixel data multiplied by the gain-correcting value issupplied to the one-line gain detecting/correcting circuit 29.

[0039] The one-line gain detecting/correcting circuit 29 extracts thepixels at the border between the right and left channel, for every line.The circuit 29 then detects the gain difference between the pixels atthe border and corrects the gain difference. The one-line gaindetecting/correcting circuit 29 can correct the gain of both channelsfor one line, thereby eliminate the gain discontinuity at the borderbetween the right and left channel for each line. The pixel data, thusgain-corrected for each line, is supplied to the delay line 30. Anexample of an operation that the circuit 29 performs will be explainedlater.

[0040] The delay line 30 delays the image data by a prescribed time sothat Y/C separation may be accomplished later. The pixel data delayed bythe delay line 30 is sent to the Y/C separating circuit 31.

[0041] The Y/C separating circuit 31 receives the pixel data input as aRGB signal or a complementary color signal. It separates the imagesignal into a luminance (Y) component and a chroma (C) component. Theluminance (Y) component is supplied to the Y process circuit 32, whereasthe chroma (C) component is input to the C process circuit 33.

[0042] The Y process circuit 32 carries out a prescribed process on theluminance (Y) component and outputs luminance data. The C processcircuit 33 effects a specific process on the chroma (C) component andoutputs chroma data.

[0043] In the image-signal processing apparatus 1 thus structured, thepixel data output from the CCD image sensor 10 in the left and rightchannels is converted to digital data for every channel. This can lowerthe operating frequencies of both analog front-end circuits 21 and 22.The apparatus 1 can, therefore, performs a stable operation.

[0044] (Plural-Line Gain Detecting Circuit)

[0045] The plural-line gain detecting circuit 23 will be described indetail, in terms of configuration.

[0046] As FIG. 4 depicts, the plural-line gain detecting circuit 23comprises a right-channel black-level correcting section 41, again-correcting section 42, a right-channel, border pixel extractingsection 43, a right-channel data integrating section 44, a left-channelblack-level correcting section 45, a left-channel, border pixelextracting section 46, a left-channel data integrating section 47, and again-detecting section 48.

[0047] The right-channel black-level correcting section 41 receives theright-channel pixel data and the right-channel black-level correctingvalue obtained by the right-channel black-level detecting circuit 24.The right-channel black-level correcting section 41 effects offsetaddition, adding the right-channel black-level correcting value to theright-channel pixel data. The section 41 thereby corrects theright-channel black level. Similarly, the left-channel black-levelcorrecting section 45 receives the left-channel pixel data and theleft-channel black-level correcting value obtained by the left-channelblack-level detecting circuit 25. The left-channel black-levelcorrecting section 45 effects offset addition, adding the left-channelblack-level correcting value to the left-channel pixel data. The section45 thereby corrects the left-channel black level. Thus, the black levelof the pixel data for both channels is corrected before the gaindifference between channels is obtained. This makes it possible todetect an accurate gain difference, with the black levels for thechannels rendered identical. The pixel data, whose black level has beencorrected by the right-channel black-level correcting section 41 issupplied to the gain correcting section 42. Meanwhile, the pixel data,whose black level has been corrected by the left-channel black-levelcorrecting section 45 is supplied to the left-channel, border pixelextracting section 46.

[0048] The gain correcting section 42 receives the right-channel pixeldata whose black level has been corrected, and also the gain-correctingvalue that has been obtained by the gain-detecting section 48. Thegain-correcting section 42 multiplies the right-channel pixel data bythe gain-correcting value, thereby correcting the gain of theright-channel pixel data. The gain is detected after it is thuscorrected. Therefore, either the increment or decrement of thegain-correcting value thus far found can be output as correcting data,not detecting the gain from the initial value. Hence, the integratingsections 44 and 47 and the gain detecting section 48 at the subsequentstages can be simplified in both circuit configuration and operationscheme. The right-channel pixel data, whose gain has been corrected bythe gain correcting section 42, is supplied to the right-channel, borderpixel extracting section 43.

[0049] The right-channel, border pixel extracting section 43 and theleft-channel, border pixel extracting section 46 extract only pixels atthe border between the right and left channels. These pixels areextracted so that the difference between the right-channel image and theleft-channel image may not influence the accuracy of the gain differencebetween channels, which is to be detected. This is because the pixels atthe border are intensely correlated, or have but an extremely smalldifference, in terms of image characteristic. The right-channel, borderpixel extracting section 43 and the left-channel, border pixelextracting section 46 extract, for example, two columns of pixels each.As FIG. 5 shows, the section 43 extracts the two columns of pixels, onthe right of the border line, and the section 46 extracts the twocolumns of pixels, on the left of the border line. The border pixel dataof the right channel is supplied to the right-channel data integratingsection 44, whereas the border pixel data of the left channel issupplied to the left-channel data integrating section 47.

[0050] The right-channel data integrating section 43 and theleft-channel data integrating section 46 integrate the border pixel datathus extracted, for all lines in the vertical direction. The integrationthey perform is given by the following equation (1):

S _(m)=(1/2^(n))I _(m)+((2^(n)−1)/2^(n))S _(m−1)  (1)

[0051] where I is the value of a pixel of the border pixel data input, Sis the result of integration, and n is the time constant of integration.The subscript to I and S is the serial number of the border pixel dataitem.

[0052] The equation is solved by hardware, more precisely an operationcircuit 50 illustrated in FIG. 6.

[0053] In the operation circuit 50, the border pixel data I_(m) is inputto the first multiplier 51. The first multiplier 51 multiplies theborder pixel data I_(m) by 1/2^(n) and outputs the product“(1/2^(n))I_(m)”. The output of the first multiplier 51 is input to thefirst adder 52. The first adder 52 adds the value “(1/2^(n))I_(m)”output from the first multiplier 51 and the value“((2^(n)−1)/2^(n))S_(m−1)” stored in the first latch circuit 53, therebyobtaining an integrated value S_(m). The integrated value S_(m) thusobtained is stored into the second latch circuit 54. The integratedvalue S_(m) stored in the second latch circuit 54 is transferred to thethird latch circuit 56 via the first switch 55 that is switched inaccordance with the timing of acquiring the integrated value. Theintegrated value S_(m) stored in the third latch circuit 56 istransferred to the fourth latch circuit 57. The value S_(m) stored inthe fourth latch circuit 57 is output from the operation circuit 50. Theintegrated value S_(m) stored in the fourth latch circuit 57 isprocessed by the second multiplier 58 and the second adder 59, whichcooperate to calculate the value “((2^(n)−1)/2^(n))S_(m)”. This value isstored into the first latch circuit 53 and will be used as value“((2^(n)−1)/2^(n))S_(m−1)” when the next border pixel data I_(m) isinput.

[0054] In the operation circuit 50, a time constant n input from anexternal device sets the multipliers 1/2^(n) of the multipliers 51 and52. The time constant n is, for example, a programmable one. Therefore,the speed at which the integrated value S converges can be changed. FIG.7 is a graph showing how this speed changes when I=100.

[0055] The integration circuit 50 has a switch 60 for setting an initialintegrated value. Once the initial integrated value is set, the time theintegrated value requires to become stable can be shortened.

[0056] The right-channel data integrating section 43 and theleft-channel data integrating section 46 output the right-channelintegrated value and the left-channel integrated value, respectively, ashas been described above. The right-channel integrated value and theleft-channel integrated value are supplied to gain-detecting section 48.

[0057] The gain detecting section 48 compares the right-channelintegrated value with the left-channel integrated value. The section 48increases or decreases the gain-correcting value in units of counts, inaccordance with which integrated value is greater than the other.

[0058] The gain detecting section 48 can be configured as is shown inFIG. 8. In the gain detecting section 48 of FIG. 8, the comparator 61compares the right-channel integrated value with the left-channelintegrated value. The result of the comparison is given to the controlcircuit 62. The control circuit 62 changes over the switch 64 at everygain-acquiring timing. The gain-correcting value stored in the outputlatch circuit 63 is thereby fed back to the −1 adder 65, +1 adder 66 andthe ±0 adder 67. The gain-correcting value is therefore increased ordecreased in units of ±1. This sequence of operations is carried out inthe gain-detecting section 48 to detect the gain, always in accordancewith the output signal of the CCD image sensor 10. In the gain detectingsection 48, the switch 68 is changed over at the time of starting thegain detection. The section 48 can therefore output a preset initialvalue as the gain-correcting value. This helps to reduce the time thatthe gain-correcting value needs to converge to a stable value.

[0059] As indicated above, the plural-line gain detecting circuit 23finds the average of the right-channel pixel data for a plurality oflines and the average of the left-channel pixel data for a plurality oflines. The circuit 23 then finds the difference between these averages,obtaining the gain difference between the right and left channels.

[0060] (Pixel-Rearranging Circuit)

[0061] The pixel-rearranging circuit 26 will be described in detail.

[0062] The pixel-rearranging circuit 26 synthesizes pixel data trainsfor two channels, i.e., the right-channel pixel data and theleft-channel pixel data, and generates one-channel pixel data train.

[0063] For example, the pixel-rearranging circuit 26 uses a memory thathas two input ports and one output port as shown in FIGS. 9A and 9B.Using the memory, the circuit 26 rearranges the pixels, thus convertingthe two-channel pixel data to one-channel pixel data train.

[0064] As FIG. 9A shows, the circuit 26 writes the right-channel pixeldata and the left-channel pixel data, line by line, into the memorythrough two independent input ports.

[0065] As FIG. 9B depicts, the circuit 26 first reads the pixel dataitems for the 0th line of the right channel, in the same order they havebeen written into the memory. Then, it reads the pixel data items of thepixel data for the 0th line of the left channel, in the order reverse tothe order they have been written into the memory. Next, it reads thepixel data items for the 1st line of the right channel, in the sameorder they have been written into the memory. Further, it reads thepixel data items for the 1st line of the left channel, in the orderreverse to the order they have been written into the memory. In thisway, the circuit 26 reads the right-channel read addresses and theleft-channel read addresses alternately, in units of half lines. Thus,the circuit 26 provides pixel data items arranged in the order a CCDimage sensor of one-channel output type scans the image on the screen.The data must be read at a rate that is at least twice the write rate.

[0066] (One-Line Gain Detecting/Correcting Circuit)

[0067] The one-line gain detecting/correcting circuit 29 will bedescribed.

[0068] The one-line gain detecting/correcting circuit 29 is a circuitthat extracts the pixels at the border between the right and leftchannels, for every line, then detects the gain difference between theright-channel pixel data near the border and the left-channel pixel datanear the border, and finally corrects the gain difference.

[0069] The one-line gain detecting/correcting circuit 29 extracts pixelsnear the border between the channels, for every line, as is illustratedin FIG. 10. In this case, the circuit 29 extracts in units of eightpixels, for the right channel and the left channel. The circuit 29 findsthe average of the pixel values for the right channel and the average ofthe pixel values for the left channel. In accordance with the ratiobetween these averages, the circuit 29 lowers the level of pixels if thechannel has a large gain, and raises the level of pixels if the channelhas a small gain. Thus, the circuit 29 reduces the gain difference atthe border between channels. For instance, the pixels near the bordermay be more corrected than the pixels far from the border, therebyminimizing the inter-channel level difference observed at the borderbetween channels.

[0070] The gain difference between channels is thus corrected for eachline. The gain discontinuity at the border between the right and leftchannels, occurring for each line, can be eliminated.

[0071] In the image-signal processing apparatus 1 according to thepresent embodiment, the black level of the pixel data of one channel,output from the CCD image sensor 10 that outputs pixel data in twochannels, is detected and corrected independently of the black level ofthe pixel data of the other channel. Further, the gain differencebetween the channels is detected and corrected. The image-signalprocessing apparatus 1 can therefore correct, with high precision, theblack levels of the right-channel and left-channel pixel data items andthe gain difference between channels.

[0072] In the image-signal processing apparatus 1, the inter-channelgain differences for a plurality of lines are detected and averaged,thereby correcting the gain difference between channels. Theimage-signal processing apparatus 1 can therefore correct the gaindifference with high accuracy.

[0073] In the image-signal processing apparatus 1, the border betweenthe right and left channel and the pixels near the border are extracted,thereby detecting the gain difference between channels from the pixelsthus extracted and correcting the gain difference between channels. Thepure gain-difference component that contains no image components cantherefore be detected in the image-signal processing apparatus 1. Hence,the gain difference between channels can be corrected with higherprecision.

[0074] Industrial Applicability

[0075] In the image-signal processing apparatus according to the presentinvention, the black levels of the pixel data items output from an imagesensor for a plurality of channels are detected and correctedindependently of one another, and the gain difference between channelsis detected and corrected.

[0076] Therefore, the image-signal processing apparatus of thisinvention can correct not only the black levels of the channels of theimage sensor, but also the gain difference between channels, with highaccuracy.

[0077] Further, in the image-signal processing apparatus according tothe invention, the average of the pixel data items for a plurality oflines is obtained, the gain difference between channels is detected andcorrected.

[0078] The image-signal processing apparatus of this invention cantherefore correct the gain difference with a higher accuracy.

[0079] Moreover, in the image-signal processing apparatus of theinvention, the border between any two adjacent channels is detected andthe data items representing pixels near the border is extracted when theimage sensor outputs pixel data items in a plurality of channels foreach line. The gain difference between channels is detected from thepixel data items extracted and then is corrected. Hence, theimage-signal processing apparatus can detect a pure gain-differencecomponent that contains no image components. This makes it possible tocorrect the gain difference between channels with higher precision.

1. An image-signal processing apparatus for processing the signalsoutput from an image sensor that reads pixel data for one screen, lineby line, divides the pixel data into a plurality of channels and outputsthe pixel data thus divided, said apparatus comprising: black-levelcorrecting means for detecting the black level of the pixel data itemfor each channel, read from the image sensor, and for correcting theblack level of the pixel data item for each channel; and gain correctingmeans for detecting and correcting the gain difference between the pixeldata items for different channels, read by the image sensor.
 2. Theimage-signal processing apparatus according to claim 1, wherein the gaincorrecting means finds an average of the pixel data items for aplurality of lines, detects the gain difference between channels andcorrects the gain difference between channels.
 3. The image-signalprocessing apparatus according to claim 2, wherein the gain correctingmeans programmably changes the number of lines for which pixel imagedata items are averaged.
 4. The image-signal processing apparatusaccording to claim 1, wherein the gain correcting means corrects thegain difference between channels for the pixel data corrected in termsof black level.
 5. The image-signal processing apparatus according toclaim 1, wherein the black-level correcting means applies an offset tothe pixel data items read from the image sensor, thereby to correct theblack level of each pixel data item.
 6. The image-signal processingapparatus according to claim 5, wherein the black-level correcting meansdetects the black level of the pixel data item for each channel, readfrom the image sensor, and calculates a target black level from thedifference between the preset black level corrected and the black leveldetected.
 7. The image-signal processing apparatus according to claim 1,further comprising pixel rearranging means for storing into a memory thepixel data items output for each channel, reading the pixel data itemsfrom the memory in a prescribed order and in units of screens, andoutputting one-channel pixel data.
 8. The image-signal processingapparatus according to claim 7, wherein the black-level correcting meansand the gain correcting means correct the black level and the gaindifference, respectively, which pertain to the one-channel pixel dataoutput from the pixel rearranging means.
 9. The image-signal processingapparatus according to claim 8, wherein the black-level correcting meansand the gain correcting means detect the black level and the gaindifference, respectively, from the pixel data which has yet to beconverted to one-channel pixel data by the pixel rearranging means, andcorrect the black level and the gain difference, respectively, whichpertain to the one-channel pixel data generated by the pixel rearrangingmeans.
 10. The image-signal processing apparatus according to claim 1,wherein the image sensor outputs image pixel data items in a pluralityof channels for each line, the gain correcting means detects the gaindifference between channels for each line and corrects the gaindifference between channels in accordance with the gain differencedetected.
 11. The image-signal processing apparatus according to claim10, wherein the gain correcting means detects the average of gaindifferences between channels, for a plurality of lines, corrects thegain difference between channels, detects the gain difference betweenchannels, for each line, and corrects the gain difference betweenchannels, for each line, in accordance with the gain differencedetected.
 12. The image-signal processing apparatus according to claim1, wherein the image sensor outputs pixel data items in a plurality ofchannels for each line and the gain correcting means detects the borderbetween any two adjacent channels, extracts the data items representingpixels near the border, detects the gain difference between channelsfrom the pixel data items extracted and corrects the gain differencebetween channels.